Using the database at
https://eddb.io/ I was able to find much better loops. One loop I was running gave me 800k in a round trip ON A TYPE-6, which gave me enough to upgrade quickly. It was also a straight one-hop. The particular routes change based on specific supply/demand, but the database keeps track of prices, and makes it easy to find them.
Right NOW, for example (it'll change throughout a given day), I'm looking at a run from Goddard Station in Kachian to/from Spinrad Gateway in LP 711-43.
Buy Micro Controllers at Goddard for 4908, sell at Spinrad for 6,310.
Buy Military Grade Fabric (GOOD stuff) for 642, sell at Goddard for 8,664(!!!!).
Profit is 9,424. For each space in your hold.
Have a Type-7 with 260 spaces? Total profit: 2.45 million for one round trip.
Not only that, but you can set the stations to large ships only (you can set to large or any, if you need to restrict the size). This run was for large ship docking. You can set jump distance and distance from the entry point. In this case, the systems were 22.28 LY, and the stations were 48 Ls and 156 Ls. In other words, one jump and stations next to the jump. Maybe 10 minutes per cycle. If you work almost 15 million/hour. YMMV.
I don't know if it's always been like this or not, but the dynamic loops makes for a lot better method than picking the same route.